Topology-Dependent Mechanical Failure of Knotted Polymer Chains from Reactive Molecular Dynamics

Long polymer chains are inevitably tangled in knots that compromise their mechanical strength, yet how knot complexity governs the molecular rupture mechanism remains poorly understood. Here, we study the mechanical failure of single polyethylene chains bearing knots of varying complexity (3–7 crossings) using reactive molecular dynamics simulations across multiple pulling rates. We identify a consistent three-stage failure mechanism comprising entropy-driven tightening, enthalpy-driven tightening, and bond rupture. The breaking force follows a stretched exponential decay with knot complexity, while the elastic modulus grows exponentially; topological confinement therefore plays two competing roles. Analysis of bond-breaking locations indicates a gradual crossover in the failure mechanism: knots with lower minimum crossing number (31, 41) break predominantly at the knot entrance/exit, whereas knots with higher minimum crossing number (71) rupture within the densely packed core. Bond angle analysis shows that the geometric distinction between entrance and core regions diminishes with increasing minimum crossing number, providing a structural rationale for the boundary-to-core shift and demonstrating that knot topology offers a tunable handle on both polymer strength and stiffness.